(1) Field of The Invention
The present invention relates to a traffic control system, and more particularly to a system for controlling traffic of data on a digital leased line between a public network and a subscriber system (herein after simply referred to as a subscriber).
To access a public network belonging to a telephone company through a digital leased line from a subscriber, it is preferable to be provided with various leased lines of various bit rates corresponding to the bit rates of respective subscribers.
(2) Description of The related Art
Conventionally, leased lines of 2.4 Kb/s to Kb/s, 1.5 Mb/s. 45 Mb/s and so forth have been prepared for practical use between each subscriber and a public network. Such a bit rate of a leased line, however, is insufficient for future subscriber services in which a large capacity is considered necessary.
To cope with the increase of the capacity of services, use of an optical transmission system, such as the already proposed SONET (Synchronous Optical Network) system, is proposed. When the SONET is used, an optical leased line of 600 Mbps, called OC-12, or an optical leased line of 2.4 Gbps, called OC-48, is used.
The problem to be solved by the invention is as follows. If a leased line of 1.5 Gbps, called OC-30, is preferable to a subscriber, but if only above-mentioned leased lines OC-12 and OC-48 are available, the subscriber must use leased line OC-48 with the bit rate of 2.4 Gbps because the other leased line OC-12 with the bit rate of 600 Mbps has too low a bit rate for the subscriber. In this case, when a telephone company provides digital service line OC-48 to the subscriber, the public network must always transmit the digital data line OC-48 from the subscriber.
The line capacity of the OC-48 line of 2.4 Gbps is the bit rate of the "maximum use amount". Therefore, all data frames are not always used by a subscriber. Namely, there is the case when Only the data amount corresponding to the OC-1 line with a bit rate of 51.84 Mbps is used or there may be the case when no data frame is used, e.g., during night. In such a case, however, under the current service condition, since it is impossible to distinguish the data frame being used and the data frame not being used, all data frames must be transmitted through the public network without conditions even when the data frame does not include traffic data.
Accordingly, for the telephone company that has a public network, it is wasteful to transmit frames without traffic data, and this is one of the reasons for not increasing the use efficiency of the public network.
Also, for the subscriber, it is not economicalto pay 100 % when 100 % of the line is not being used.